1. Field of the Invention
The present invention relates generally to liquid processing systems and methods, and particularly to a method of solvent recovery from a dilute solution.
2. Description of the Related Art
Many solutions that exist in nature or that are produced by industrial processes or as waste streams are dilute. Sea water, for example, includes 3%-5% salts and 95%-97% water, while brackish water contains much more water and less dissolved solids. Conventional desalination of sea or brackish water is an energy intensive process that has a low recovery ratio and produces large amounts of effluents that have a negative impact on the environment. Milk includes 87%-91% water, and fruit and vegetable juices usually include 80%-95% water. The conventional process for concentrating milk, coffee extract, and juices to a high concentration utilize membrane processes having low recovery ratios or do not concentrate the streams to a high solute concentration.
One of the most common technologies used in solvent purification and concentrating dilute solutions is that of reverse osmosis (RO), where a solvent is forced through a permeable membrane from a region of high solute concentration to a region of low solute concentration by applying a pressure greater than osmotic pressure. However, conventional reverse osmosis (RO) processes suffer from certain challenges that include low recovery ratio and membrane scaling. These two challenges control the economics of RO desalination and concentrating dilute solutions and both of them are related to pressure across the membrane. Higher recoveries can be obtained by increasing the pressure across the membrane. However, such increase in pressure causes (1) higher scale formation that is promoted by compaction and (2) higher solute concentration in the concentrate side of the membrane. In addition, increased pressure across the membranes requires costly membrane assemblies and higher power consumption.
A number of liquid purification systems have been developed in the past. An example of such is found in European Patent Publication No. 1,020,407 published on Jul. 19, 2000 to Uwatech GMBH et al. This reference describes (according to the drawings and English abstract) treating condensate effluent containing ammonium nitrate by successive reverse osmosis to yield a process water stream and a concentrate which is recycled.
Thus, a method of solvent recovery from a dilute solution solving the aforementioned problems is desired.